The first sentence in the Wikipedia article: "Andrea Rossi (born 3 June 1950) is an Italian convicted fraudster, inventor and entrepreneur." (Though the footnote to "fraudster" indicates he was ultimately acquitted, on what appears to be a technicality, of the major charges relating to an alleged oil-from-trash scam.) The best you can say about E-Cat is that Rossi seems to be doing everything possible to make it look like a scam (Starts with a Bang.)
Rossi's E-Cat was the first thing I thought of when I read of Gates trip to Italy, but he was apparently visiting the Frascati ENEA labs of the University of Verona, which is "recognized for excellence in [cold] nuclear fusion research", whatever that means. I do not know if it has any connection to Rossi.